Plants "breathe in" CO2 and create biological mass. This is a form of sequestration. Forests, grasslands and shrublands and other ecosystems in the West sequester nearly 100 million tons of carbon each year, according to a Department of the Interior recent report. Grasslands occur naturally on all continents except Antarctica. In temperate latitudes, such as northwestern Europe and the Great Plains and California in North America, native grasslands are dominated by perennial bunch grass species, whereas in warmer climates annual species form a greater component of the vegetation. Carbon that is absorbed through natural processes reduces the amount of carbon dioxide in the atmosphere. The 100 million tons sequestered in western ecosystems is an amount equivalent to — and counterbalances the emissions of — more than 83 million passenger cars a year in the United States, or nearly 5 percent of EPA’s 2010 estimate of the nation’s total greenhouse gas emissions.

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"This important study confirms the major role that our natural landscapes have in absorbing carbon and helping to counter-balance the nation’s carbon emissions," said Deputy Secretary of the Interior David J. Hayes. "This kind of groundbreaking science not only will help us be more effective stewards of our lands, but it also helps reveal how our forests, wetlands and range lands in the West — and throughout the nation — are positively impacting the carbon cycle."

The report, authored by U.S. Geological Survey scientists, is part of a national assessment of carbon storage and sequestration capacities by ecosystems. This assessment estimates the ability of different ecosystems in the West to store carbon — information that will be vital for science-based land-use and land-management decisions. The first report, on the Great Plains, was released in December 2011; reports on the eastern United States, Alaska, and Hawaii will follow.

The area includes well-known ecosystems, such as the Rocky Mountains and the Sierra Nevada Mountains, the Mojave and Sonoran deserts, the Pacific Northwest forests and the vast grasslands and shrublands of the Great Basin. The study’s results point out that these lands are immensely valuable because of their ability to store carbon.

"This report contains 12 original chapters of new science that will enable land managers to track and calculate carbon storage and greenhouse gas fluxes over time for the American West's varied ecosystems," said USGS Director Marcia McNutt. "With more than 300 references of the latest work relevant to how biological systems cycle carbon, this report is a scientific tour de force."

Terrestrial ecosystems accounted for more than 95 percent of the estimated total carbon sequestered between 2001 and 2005 in the West. Although the ecosystems varied widely in their potential to store, the study found that forests are by far the largest carbon-storing pools, accounting for about 70 percent of the carbon stored in the West. Forests occupy 28 percent of the land in the West, contain the most carbon per unit area, and have the second-highest rate of sequestration of ecosystem types. Wetlands had the highest rate of sequestration of all ecosystem types, but because they cover less than 1 percent of the West, the amount of carbon they sequester is far less significant from a regional perspective.

Grasslands and shrublands also store a lot of the West’s carbon: this land type covers nearly 60 percent of the West and contains 23 percent of the region’s carbon stored between 2001 and 2005. Agricultural lands, which comprise about 6 percent of the West, contain 4.5 percent of the carbon stored during the same period.

Other major findings of the report included:

Wild land fires generated significant amounts of greenhouse gas emissions in the West, with such emissions equivalent to 13 percent of the estimated rate of the recent annual carbon sequestration by terrestrial ecosystems in the West.

Water bodies in the western United States emitted even more CO2 than fires. Emissions from water bodies are equivalent to more than 30 percent of the recent annual carbon sequestration rate of terrestrial ecosystems in the West.

The western report is the second in a series of reports produced by USGS for a national assessment of carbon storage and flux, and fluxes of other greenhouse gases.